A driving device is well known in which the alternating current voltage is applied to a piezoelectric element so that a vibrating section is oscillated, and the vibrating section is repeatedly brought into contact with or separated from members to be shifted, whereby the members can be shifted by friction force. A lens barrel is also well known in which above driving device is used for shifting the lens units.
As a driving device, which uses the piezoelectric element to shift lens units along the optical axis, a lens driving device is disclosed in which a vibrator to create driving vibration along the optical axis is pressed by an elastic member against a guide shaft, which is a stationary part prolonging along the optical axis, and the vibrator is assembled in a lens supporting member (see Patent Document 1)
[Patent Document 1] Unexamined Japanese Patent Application Publication 8-179184
However, the lens driving device of Patent Document 1 features the vibrator in the lens supporting member, and the vibrator is pressed against a guide shaft, which guides the lens supporting member along the optical axis, via the elastic member. Accordingly, due to the reaction force of pressing force caused by the elastic member, the guide shaft is off-center in the hole of the lens supporting member. Consequently, friction increases between the hole of the lens supporting member and the engaging guide shaft, and off-center abrasion is created in the hole of the lens supporting member, which results in unstable movement, and further, the position of the lens units is shifted in the direction perpendicular to the optical axis by the off-center abrasion of the hole, resulting in deterioration of the desired lens characteristics.
Further, since the movement of the lens units by the vibrator is conducted due to the friction force, the friction force between the hole of the lens supporting member and the engaging guide shaft works in the direction to reduce the driving force of the vibrator, which results in the reduction of the driving efficiency of the vibrator, and further the change of the friction force between the hole and the guide shaft triggers unstable movement.
This problem happens by the reaction force of the elastic member, even when the stationary part is separated from the guide shaft, as a separated structure.